Pennsylvania is the best state for Fall fun (not that I'm biased...), however, it can be hard to decide what to do with the many activities going on. As a native Pennsylvanian, I have experienced or heard of many of these. I will give you my top recommendations based on activities I've found fun. Also included will be activities that have been recommended to me.
1. Go to an Orchard
The closest orchard to me is Highland Orchards in West Bradford Township, PA, but Southeastern PA boasts many more including Linvilla Orchards of Media, PA and North Star Orchard in Cochranville, PA. During the Fall season, many of these Orchards offer a variety of fun activities for couples, families, and people of all ages. Highland offers apple picking shuttles out to the fields where you can pick a peck of everything from Gala to Mutsu and Jonagold. If you like your apples in a less solid form, they offer warm apple cider inside, and you can pair it with one of their mind-blowing apple cider donuts. They also offer a family fun area where kids and parents alike can make a scarecrow or go through a hay maze. Occasionally throughout the season, they offer a late night hayride great for couples and for families. Sometimes this is paired with a bonfire and a spooky story, especially as it nears Halloween. If you're already dreaming of Thanksgiving, you can pre-order your pies for the big day and pick them up the day before.
2. Enjoying a Picnic at the Park
Pennsylvania is a very green state that has many parks, state and local. Any of the many locales would be a prime spot to go on a romantic picnic or even just a family outing. Brandywine Picnic Park in West Chester, PA also offers games and pedal boats that you can take on the Brandywine River that runs nearby. Valley Forge State Park in Valley Forge, PA is not only a great picnic spot but a historical one as well. If you are a history buff this park is the place for you. Check out their website to find out more about their historical tours here: https://www.nps.gov/vafo/planyourvisit/historictales.htm
3. On that note...
Pennsylvania is a pinnacle of history thanks to our revolutionary friends. The mecca for it in Southeast PA is in the historic city of Philadelphia. There you can visit the home of the liberty bell and the constitution, and see where Betsy Ross embroidered the first flag of our country. If revolutionary history is not your thing, Eastern State Penitentiary is a more recent blast from the past that played host to Al Capone and others. Not only is it a piece of history, it is also a local haunt during the Halloween season.
4. Halloween Haunts
As mentioned above, Eastern State is a popular haunted attraction. Hell, I went for one of their daytime historical tours and I still felt spooked. Another popular locale is Pennhurst Asylum. Many a college friend would return from this one looking as if they'd gotten an email about a surprise exam from a professor. Then if you travel just up Route 3 and head toward the Granite Run area you run into the Bates Motel, home of the haunted hayride. Lastly is Jason's Woods, another popular fright that lives in the heart of Lancaster, PA.
5. Intercourse, PA
Despite the town name that incites inappropriate giggles, this small town is no laughing matter when it comes to what is offered in the village here. Kitchen Kettle Village boasts several shops with everything from olive oil, leather jackets, fudge, preserved bugs and music boxes. That only scrapes the surface of what is offered there. It is a locale you could visit several times and come home with something new each trip. Nearby is Rumspringa Brewery that has a plethora of wines, beers, and ciders to choose from. You can get a growler or just a glass to sit and enjoy.
Also in Lancaster County is the Strasburg Railroad Line which offers a variety of tours and activities including a haunted train ride, a train robbery, and a wine and paint night for the adults. Also offered is the West Chester Railroad Company that offers Fall foliage tours and a Halloween themed ride, great for families with small kids.